Dispatch services, also known as walkie-talkie services, provide near-instant, half-duplex communication between a dispatch caller and one or more target dispatch users. Dispatch services are typically offered as subscription services on wireless communications systems, which may also offer interconnect calling, short message service (SMS), packet data and other communications services to wireless subscribers. Each wireless communications system facilitates communications using one or more multiple-access wireless technologies such as code division multiple access (CDMA), global system for mobile communication (GSM), time division multiple access (TDMA), orthogonal frequency division multiplexing (OFDM), and others. Known dispatch technologies include Nextel's Direct Connect®, Qualcomm's QChat and Push-to-Talk over Cellular (PoC).
Existing dispatch services were optimized to minimize communications latencies to achieve the near-instant communications desired by dispatch subscribers. These high performance dispatch networks typically include a regional dispatch application server that manages dispatch communications for local wireless subscriber units. To initiate and receive dispatch calls in a conventional dispatch network, the wireless subscriber must first register with a regional location server and a dispatch application server servicing the network region. When the wireless subscriber roams to a different region or network, registration with the new network is required to notify the wireless subscriber's home network of its current location, and receive authorization to access local dispatch services.
Various frameworks exist for facilitating the provisioning of multimedia application services to roaming subscribers, including the IP Multimedia Subsystem (IMS) standard. IMS was developed to provide open access to a wide variety of multimedia applications across disparate communications networks and administrative location domains. A wireless subscriber roaming onto an IMS network requires a single registration as an IMS client to access available IMS applications.
Conventional high performance dispatch networks do not support IMS registration for PTT services. Accordingly, a need exists for systems and methods for implementing IMS registration on dispatch networks.